This invention relates generally to test equipment which is utilized to establish electrical contact with electrical/electronic devices during testing thereof and, more particularly, to a magnetic field generator having a plurality of vertical probe cards mounted within a central corridor or opening thereof.
Horizontal printed circuit probe cards are known in the prior art. Probe needles electrically attached to the card protrude downwardly through a hole therein to a plane in which the electronic device under test is positioned. By accurately positioning the ends of the probe needles on conductive pads of the device under test, the user may establish electrical contact therewith for the purpose of measuring certain electrical parameters thereof. Two embodiments of this prior art test method are known as the blade card implementation and the epoxy ring implementation. The blade card implementation utilizes electrically conductive blades that are soldered to the horizontal circuit card. These blades also have small needles affixed to them for the purpose of contacting test pads of the device under test by penetration through the hole in the horizontal card. The epoxy ring implementation involves probe needles accurately located and restrained by an epoxy ring. The epoxy ring is affixed to the horizontal probe card, and the individual probe needles are electrically attached thereto. The ends of the probe needles penetrate through a hole in the horizontal probe card to make electrical contact with test pads of the device under test.
Some testing processes require the addition of a magnetic field to stimulate the devices under test. As a practical matter, it is desirable to locate the magnetic field generator as close as possible to the device under test. In order to accomplish this objective, the blade or epoxy ring type of horizontal card with probe needles must not reside between the device under test and the magnetic field generator. A corridor or opening in the center of the magnetic field generator can be utilized to facilitate placement of the probing mechanism above the magnetic field generator. Although either one of the two embodiments of the horizontal probe card may be utilized in this configuration, they each have deficiencies which render them undesirable.
The blade card, when used to probe through a corridor in a magnet, is very limited in the number of probe needles it can carry due to the large space requirements of each blade. This restriction severely limits the ability of the test system to evaluate the device under test. In addition, due to the required spacing of the probes, an induced voltage will be observed when the magnetic field is applied. If this spacing were somehow reduced, the induced voltage would also be substantially reduced.
The epoxy ring card is not functional when used to probe through a corridor in a magnet due to the length requirement of the probe needles. The result is that the contact force which the longer probe needles are able to exert on the test pads of the device under test is so low as to result in poor electrical contact.
It would therefore be advantageous to provide a vertical probe card for probing a device under test through a corridor in a magnetic field generator, while locating the device under test as close to the magnetic field generator as possible. It would also be advantageous to densely locate the traces on the vertical probe card in order to reduce the effect of the magnetic field on the test measurement. An additional advantage of such a vertical probe card is to provide a rigid structure to support the probe needles just above the device under test and to provide support for long probe needles that are required to reach relatively long distances.